The present invention relates to a sample pulse generating apparatus which is adaptable, for example, for the case where wave forms of high frequency signals are observed through the observation of those analogous ones of low frequency which are transformed from the former wave forms of high frequency through sampling operation.
In observing the wave forms of high frequency signals such as pulse trains, it is common to transform the high frequency signal into a lower frequency signal having the wave form analogous to that of high frequency one, by sampling the high frequency one at a relatively low rate, as found in the sampling oscilloscope. One form of the sample pulse generators for such a sampling operation is shown in FIG. 1.
As shown in FIG. 1, a high frequency pulse train with a wave form (a) (FIG. 2(a)) is inputted into a frequency divider 1 where it is frequency-divided to have a signal wave form (b) of low frequency (FIG. 2(b) ). After being frequency-divided, the input signal is applied to a saw tooth wave generating circuit 2 and is transformed into the signal having a saw tooth wave (c) (FIG. 2(c)) in synchronism with the input signal, which in turn is fed to a voltage comparator 3.
A staircase wave generator 4, in response to the signal from the voltage comparator 3, generates a signal having a staircase wave form (d) (FIG. 2(d)) of which the level staircasely increases in synchronism with the saw tooth signal (c). The staircase waveform signal (d) is applied to the voltage comparator 3. The comparator 3 compares the level of the saw tooth wave form signal with that of the staircase waveform signal and produces pulses (e) (FIG. 2(e)) every time that those signals coincide in level with each other, the pulses being used as sampling pulses. Connecting together those sampled points forms a wave form (f) (FIG. 2(f)) with the enlarged time axis, i.e., a low repition rate, which is analogous to that of the input signal (a). This wave form of low repition rate is used for observing the input signal form (a) of high frequency.
In such as apparatus, the constancy of the sampling interval on the time axis of the wave form for observation, depends on the staircase precision of the staircase waveform and largely on the linearity of the slant portion of the saw tooth waveform signal. It is to be noted here that the saw tooth waveform shown in FIG. 2(c) is the ideal one, but, in the actual saw tooth wave form, the slant portion is not linear but slightly curved, i.e., the slant thereof in this example is more gentle with time. For this, the sampling pulse occurs, as shown by the dotted line, displaced from the predetermined position indicated by the solid line (see FIG. 2(e)). This causes deterioration of the constancy of the sampling interval.